A laboratory animal nutritional research program is being conducted with various strains and stocks of small animals maintained in conventional and specific pathogen-free environments. The primary objectives of the program are to develop and evaluate open formula rations that can be used to improve the nutritional status of animal colonies and to identify differences in nutrient requirements among various strains and stocks of animals. A series of factorial-designed feeding trails are conducted to determine the effect of varying concentrations of dietary crude protein, crude fat, crude rats, guinea pigs, and rabbits.